Department of Chemistry , Indian Institute of Technology Patna , Bihar 801106 , India.
J Phys Chem B. 2019 Aug 22;123(33):7178-7189. doi: 10.1021/acs.jpcb.9b01719. Epub 2019 Aug 13.
Some experiments have witnessed gradual decoupling of viscosity from the translational self-diffusion of supercooled water with decreasing temperature. This indicates the breakdown of the Stokes-Einstein equation in supercooled water. While some theoretical and computer simulation studies indicated the jump translation of the molecules as a probable origin of the above decoupling, direct quantitative evidence is still lacking. Through a molecular dynamics (MD) simulation study, along with careful consideration of translational jump motion, we have found the most definite proof of increasing relevance of translational jump diffusion in the above decoupling phenomena. By separating the jump-only diffusion contribution from the overall diffusion of the water, we obtain the residual diffusion coefficient, which remains strongly coupled to the viscosity of the medium at the supercooled regime. These new findings can help to elucidate many experimental studies featuring molecular transport properties, where strong diffusion-viscosity decoupling is present.
一些实验见证了随着温度的降低，超冷水中的粘度与平移自扩散逐渐解耦。这表明在超冷水中，Stokes-Einstein 方程失效。虽然一些理论和计算机模拟研究表明分子的跳跃平移是上述解耦的可能起源，但仍缺乏直接的定量证据。通过分子动力学（MD）模拟研究，并仔细考虑平移跳跃运动，我们找到了上述解耦现象中平移跳跃扩散相关性增加的最明确证据。通过将跳跃扩散与水的整体扩散分离，我们得到了剩余扩散系数，该系数在过冷状态下仍然与介质的粘度强烈耦合。这些新发现可以帮助阐明许多具有分子输运性质的实验研究，其中存在强烈的扩散-粘度解耦。
